Froth flotation is the principal means by which phosphate ores, such as pebble phosphate and apatite, and a host of other ores are concentrated. Its chief advantage lies in the fact that it is a relatively efficient process operating at substantially lower costs than many other processes capable of concentrating the ores.
Flotation is a process for separating finely ground valuable minerals from their associated gangue, or waste, or for separating valuable components one from another. In froth flotation, frothing occurs by introducing air into a pulp of finely divided ore and water containing a frothing agent. Minerals that have a special affinity for air bubbles rise to the surface in the froth and are separated from those wetted by the water. The particles to be separated by froth flotation must be of a size that can be readily levitated by the air bubbles.
Agents called collectors are used in conjunction with flotation to promote recovery of the desired material. The agents chosen must be capable of selectively coating the desired material in spite of the presence of many other mineral species. Current theory states that the flotation separation of one mineral species from another depends upon the relative wettability of surfaces. Typically, the surface free energy is purportedly lowered by the adsorbtion of heteropolar surface-active agents. The hydrophobic coating thus provided acts in this explanation as a bridge so that the particle may be attached to an air bubble. The practice of this invention is not, however, limited by this or other theories of flotation.
Typically, phosphate ore containing 15-35% BPL[bone phosphate of lime, Ca.sub.3 (PO.sub.4).sub.2 ] is concentrated in very large tonnages from deposits such as the Florida pebble phosphate deposits. The ore slurry from strip mining is sized at about 1 millimeter and the coarser fraction, after scrubbing to break up mud balls, is a finished product. The minus 1 mm fraction is further sized at 35 and 200 mesh. The minus 200 mesh slime is discarded. From the sizing operation, the .+-.35 mesh material in thick slurry is treated with fatty acid, fuel oil, and caustic, ammonia or other alkaline material and the resulting agglomerates are separated on shaking tables, spirals, or spray belts. The 35.times.200 mesh fraction is conditioned with the same type of reagents and floated by conventional froth flotation routes. Not all the silica gangue is rejected by the fatty acid flotation so the concentrate is blunged with acid to remove collector coatings, deslimed, washed free of reagents and subjected to an amine flotation with fuel oil at pH 7-8. This latter flotation, sometimes called "cleaning", removes additional silica and raises the final concentrate grade to 75-80% BPL.
Although the procedure described is effective in the beneficiation of phosphate ores in general, there, nevertheless, exists the need for more effective collectors which provide increased recovery of phosphate minerals while still providing high grade. It is particularly desirable to reduce the requirements for fatty acids which are constantly being diverted to nutritional and other uses. In view of the high quantities of phosphate minerals processed by froth flotation, such a development can result in a substantial increase in the total amount of mineral values recovered and provide substantial economic advantages even when a modest increase in recovery is provided. It is also highly desirable to have an efficient collector system for use at reduced dosage levels without sacrificing the mineral recovery performance. The decreases in reagent consumption are significant in view of the increasing diversion of fatty acids to nutritional and other uses.
Accordingly, the provision for an improved process for beneficiating phosphate minerals would fulfill a long-felt need and constitute a significant advance in the art.